In a typical wireless communication system, a base station (BS) provides services to a plurality of user equipments (UEs). The BS schedules user data on the plurality of UEs, and transmits control information together with the user data. The control information contains scheduling information regarding the user data. A channel for carrying the control information is generally referred to as a control channel. A channel for carrying the user data is generally referred to as a data channel. The UE monitors the control channel to find control information of the UE, and processes data of the UE by using the control information. Monitoring is an operation in which the UE attempts to decode control channel candidates.
In order for the UE to receive the user data allocated to the UE, the control information regarding the user data on the control channel must be received. In general, a plurality of pieces of control information of the plurality of UEs are multiplexed within one transmission interval in a given bandwidth. That is, to provide a service to the plurality of UEs, the BS multiplexes the plurality of pieces of control information of the plurality of UEs and transmits the control information through a plurality of control channels. Each UE finds its own control channel from the plurality of control channels.
Blind decoding is one of schemes for detecting specific control information from a plurality of pieces of multiplexed control information. The blind decoding is performed by the UE to recover a control channel by combining a plurality of pieces of information in a state where information required to recover the control channel does not exist. That is, in a state where the UE neither knows whether a plurality of pieces of control information received from the BS is control information of the UE nor knows in which location the control information of the UE exists, the UE decodes all pieces of provided control information until the control information of the UE is detected. The UE may use its unique information to determine whether the received control information is control information of the UE. For example, when the BS multiplexes control information of each UE, the BS may transmit a unique identifier of each UE by masking the identifier onto a cyclic redundancy check (CRC). The CRC is a code used in error detection. The UE demasks its unique identifier with the CRC of the received control information, and thereafter can determine whether the received control information is control information of the UE by performing CRC checking.
If the UE does not correctly detect its control information from the plurality of pieces of multiplexed control information, the UE cannot decode user data on a data channel. Therefore, it can be said that rapid and accurate detection on control information has a significant effect on overall system performance. However, it may be difficult to detect the control information by using only simple blind decoding.
Each UE may require different control information and may use a channel encoding scheme using a different code rate. Thus, a size of control information may be different from one UE to another. Consequently, the number of blind decoding attempts may be unexpectedly increased in a control region where control information is transmitted. Battery consumption of the UE increases in proportion to the number of detection attempts.
Accordingly, there is a need for a method of effectively monitoring a control channel, whereby control information is rapidly detected by decreasing the number of detection attempts to reduce battery consumption of a UE.